Nylofume® bags are the ideal waterproof pack liner. Made from a nylon polymer film, they are tough and lightweight. Being fully transparent means it's easy to find your gear. You can close the bag like I did in the photo, or use an elastic or just roll them up. Duct tape is good for repairs. 

By using two pack liners in your pack, your quilt and clean clothing can be separated from other gear, and both bags are easily removed from the pack when setting up camp.